Apparatus and method for controlling transmission in a communication system

ABSTRACT

The invention provides a communication system and components thereof for controlling coordinated transmissions using a plurality of carriers operated by a plurality of transmission points. A transmission point configures a number of signal quality and interference measurements for a mobile telephone communicating over the plurality of carriers, each measurement being associated with multiple carriers and multiple measurement configurations. The mobile telephone performs the configured measurements with respect to each of the multiple carriers and reports the results of the relevant measurements to the transmission point.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation application of Ser. No.16/666,526 filed on Oct. 29, 2019, which is a Continuation applicationof Ser. No. 16/002,083 filed on Jun. 7, 2018, U.S. Pat. No. 10,511,371issued on Dec. 17, 2019, which is a Continuation Application of Ser. No.14/768,513 filed on Aug. 18, 2015, U.S. Pat. No. 10,003,391 issued onJun. 19, 2018, which is a National Stage Entry of InternationalApplication PCT/JP2014/059904 filed on Mar. 28, 2014, which claims thebenefit of priority from United Kingdom Patent Application 1306100.7,filed on Apr. 4, 2013, the disclosures of all of which are incorporatedin their entirety by reference herein.

TECHNICAL FIELD

The present invention relates to a communication system and tocomponents thereof for providing communication services to mobile orfixed communication devices. The invention has particular, but notexclusive, relevance to cell signal measurements and channel stateinformation reporting in Long Term Evolution (LTE) Advanced systems ascurrently defined in associated 3rd Generation Partnership Project(3GPP) standards documentation.

BACKGROUND ART

In a cellular communications network, user equipment (UE) (such asmobile telephones, mobile devices, mobile terminals, etc.) cancommunicate with other user equipment and/or remote servers via basestations. LTE systems include an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN) and an Evolved Packet Core (EPC) network (orsimply ‘core network’). The E-UTRAN includes a number of base stations(‘eNBs’) for providing both user-plane (e.g. Packet Data ConvergenceProtocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC)and PHYsical (PHY) layers) and control-plane (e.g. Radio ResourceControl (RRC)) protocol terminations towards the UE.

Depending on various criteria (such as the amount of data to betransmitted, radio technologies supported by the mobile telephones,expected quality of service, subscription settings, etc.), each basestation is responsible for controlling the transmission timings,frequencies, transmission powers, modulations, etc. employed by themobile telephones attached to the base station. In order to minimisedisruption to the service and to maximise utilisation of the availablebandwidth, the base stations continuously adjust their own transmissionpower and also that of the mobile telephones. Base stations also assignfrequency bands and/or time slots to mobile telephones, and also selectand enforce the appropriate transmission technology to be used betweenthe base stations and the attached mobile telephones. By doing so, basestations also reduce or eliminate any harmful interference caused bymobile telephones to each other or to the base stations.

In order to optimise utilisation of their bandwidth, LTE base stationsreceive periodic signal measurement reports from each served mobiletelephone (based on measurement configurations provided by the E-UTRAN),which include information about the perceived signal quality on a givenfrequency band used by (or being a candidate frequency band for) thatmobile telephone. The served mobile telephones carry out measurements onreference signals that are transmitted at a known (non-zero) powerlevel. By comparing the received power level to the reference powerlevel, they are able to establish a measure of the signal degradationbetween the base station transmitting and the mobile telephone receivingthe signal. On the other hand, interference is usually measured onresource blocks where transmissions of the serving base station aremuted (i.e. set to zero power). That way, any signal that can bedetected by the mobile telephone whilst the base station is known totransmit at zero power can be classified as interference caused by othertransmitters operating in the same frequency band (e.g. neighbouringbase stations and/or other mobile telephones). Depending on themeasurement configurations (which are provided by the E-UTRAN), themobile telephones generate and send measurement reports to their servingbase stations. The measurement reports may be sent either periodicallyor when predefined events occur (e.g. interference gets higher than apredetermined threshold, signal quality falls below a predeterminedlevel, etc).

These signal measurement reports are then used by the base stations intheir decision to allocate certain parts of their bandwidth to theserved mobile telephones and/or to adjust their transmission powerand/or to hand over mobile telephones to other base stations (or otherfrequency bands/other radio access technologies (RATs)) when the signalquality does not meet the established criteria. The handing over of amobile telephone might be necessary, for example, when the mobiletelephone has moved away from the given base station, and also when asignal quality/interference problem has arisen.

A so-called Downlink Coordinated Multi-Point (CoMP)transmission/reception feature was introduced in Rel-11 of the 3GPPstandards documentation to improve, for example, the coverage of highdata rates for user equipment, temporary network deployment, cell edgethroughput and/or to increase system throughput. The CoMP featureestablished techniques for compatible mobile telephones (and other userequipment) to communicate with multiple transmission points (TPs),substantially simultaneously. The TPs typically include (any combinationof) base stations (eNBs), remote radio heads (RRHs), relay nodes (RNs),and the like. These techniques are described in, for example, TR 36.819V11.1.0, the contents of which are hereby incorporated by reference. Insummary, CoMP may be used i) to optimise received signal quality at themobile telephone by transmitting the same signal from multiple TPsand/or ii) to increase data throughput by sending different signals(e.g. different parts of the user data) from different TPs concurrently(but of course without causing interference, e.g. by using differentfrequencies/timing/codes/etc).

When multiple transmission points are used by the mobile telephone, itis configured to measure and report the quality of the signalstransmitted by each transmission point and also to measure and reportback any interference experienced so that each transmission point canadjust its operation accordingly (i.e. to be able to transmit at/near anoptimum power level and to keep interference to a minimum). Since themobile telephone in this case is located within the overlapping coverageareas (cells) of multiple transmission points, these transmission pointsneed to coordinate the transmissions of their reference signals, inorder to make it possible to carry out the above described signalquality and interference measurements. In particular, when CoMP is used,the different transmission points transmit their respective referencesignals at different times (whilst the other transmission points aremuted), one by one, so that signal quality can be measured effectivelyby the mobile telephone, for each transmission point. Additionally, inorder for the mobile telephone to able to measure interference caused byother transmitters than the cooperating transmission points, the basestations need to be muted, temporarily, at the same time, at least forthe duration of the mobile telephone's measurements. Thus, the number ofmeasurements (to be configured for and performed by the mobiletelephone) equals to the number of transmission points (each one being ahypothetical interfering TP) plus one (for determining interferencecaused by other transmitters).

In Release-11, downlink CoMP has been specified to allow multipletransmission points (e.g. base stations) to coordinate their downlinkdata transmissions. In order to support more efficient utilisation ofthe downlink resources, the mobile telephone may be configured to reportchannel state information (CSI) by measuring a set of non-zero power(NZP) reference signal (RS or CSI-RS) resources—this set is known as theCoMP measurement set. For example, the mobile telephone may carry outmeasurement of a reference signal received power (RSRP) and report theresults of this measurement to the base station which in turn can usethe measurement to adjust its operation and to manage the CoMPmeasurement set (e.g. to choose a CoMP measurement set for which CSIfeedback is required). The maximum size of the CoMP measurement set isthree NZP CSI-RS resources, selected from all possible CSI-RS resources(defined as a CoMP Resource Management Set).

The mobile telephone may also be configured to perform one or moreinterference measurements (CSI-IM). Each CSI-IM is associated with oneinterference measurement resource (IMR), which is a set of resourceelements on which interference measurements can be made.

In a so-called ‘CSI process’, the E-UTRAN can request the mobiletelephone to carry out a combined measurement on a NZP CSI-RS resourceand on an IMR. The mobile telephone performs the combined measurementson resources indicated by the ‘CSI process’, and sends a so-called ‘CSIreport’ to the E-UTRAN, which includes the results of the combinedmeasurements. The mobile telephone can be configured to perform, inresponse to a given CSI process, periodic and/or aperiodic CSIreporting.

A new LTE transmission mode (‘Transmission mode 10’ or ‘TM10’) has alsobeen defined in Rel-12 to provide support for CoMP functionalities. Therelevant parameters of transmission mode 10 are defined in 3GPP TS36.213 (v11.1.0), the contents of which are incorporated herein byreference. In particular, section 7.1 of TS 36.213 describes scramblingidentities for UE-specific reference signal generation, supported DCIformats and transmission schemes. Section 7.2 describes that a mobiletelephone in transmission mode 10 can be configured with one or more CSIprocesses per serving cell (by higher layers). Each CSI process isassociated with a CSI-RS resource (defined in Section 7.2.5) and aCSI-interference measurement (CSI-IM) resource (defined in Section7.2.6). A CSI reported by the mobile telephone corresponds to a CSIprocess configured by higher layers. Each CSI process can be configuredwith or without PMI/RI reporting by higher layer signalling.

In Rel-12, in order to enhance small cell performance, mechanisms forinterference avoidance and coordination between macro and small cells aswell as among small cells are currently being considered. However, sinceclusters of relatively small cells are typically denser than scenariosconsidered for the so-called Enhanced Inter-Cell InterferenceCoordination (enhanced ICIC or eICIC) technique in Rel-10, or for theso-called Further Enhanced ICIC (FeICIC) technique and CoMP in Rel-11,these techniques cannot be re-used without added complexity to the userequipment and/or transmission points.

Furthermore, the carrier aggregation (CA) feature defined forLTE-Advanced supports transmission bandwidths up to 100 MHz of spectrumby aggregating the resources of two or more component carriers. Whencarrier aggregation is used there are a number of serving cells, one foreach component carrier. The radio resources connection is handled by onecell, the primary serving cell, served by the primary component carrier(PCC), whilst user data may be communicated via any of the componentcarriers, primary and/or any secondary component carrier (SCC). However,the effective coverage of and/or perceived signal qualities offered bythe various serving cells may differ—either due to the differentfrequencies used in different cells or due to power planningconsiderations (and possibly other factors influencing propagation oftransmitted signals). Therefore, the base station configures the mobiletelephones it is serving via its component carriers to carry out andreport predetermined signal quality and interference measurements (i.e.one or more CSI processes, depending on the number of cells to bemeasured) so that it can take appropriate corrective actions when signaldegradation is experienced by user equipment within its cell(s).

3GPP has recently made a working assumption (at RANI meeting #71) thatfor the joint operation of downlink CoMP and CA, the UE capability forthe number of supported CSI processes is defined as follows:

-   -   P_(CSI) is the maximum number of CSI processes supported on a        component carrier;    -   P_(CSI) is provided per band combination;    -   The P_(CSI) value applies to each component carrier within a        band; and    -   P_(CSI) can take a value in {1,3,4}.

In this context, band combination refers to a collection of bands.Therefore, it can be seen that for a mobile telephone which is capableof performing up to a maximum of four simultaneous CSI processes intransmission mode 10 (for both single carrier operation and carrieraggregation), and assuming that there are five bands (componentcarriers) aggregated, this means that there is always at least one bandin which the mobile telephone cannot process any CSI processes.

SUMMARY OF INVENTION Technical Problem

In the case of joint CA and CoMP operation, the total number of CSIprocesses for CSI feedback is limited to five from all componentcarriers. This limitation was introduced in order to minimise thesignalling needed between the base station and served user equipment andthereby ensure effective utilisation of the radio interface betweenthem. However, since a maximum of five component carriers can beaggregated per transmission point, this limitation means that it is notalways possible to support CoMP operation when two or more componentcarriers are configured. Even in the case of fewer than the maximumnumber of component carriers being configured, different CoMP schemescannot always be supported simultaneously and/or adequately due to thelimited number of CSI feedback processes that are available.

The present invention aims to provide an improved communication systemand improved components of the communication system which overcome or atleast alleviate one or more of the above issues. In particular, theinvention aims to provide downlink (DL) CoMP CSI feedback and IMRmechanisms, improve support for simultaneous CoMP and CA, and/or forheterogeneous network (HetNet) services. The present invention also aimsto reduce complexity of the user equipment and the number of CSIfeedbacks required for CoMP.

Solution to Problem

In one aspect, the present invention provides a network node forcontrolling coordinated transmissions, in a communication systemcomprising at least one mobile device and a plurality of transmissionpoints which operate at least one cell, the network node comprising:means for sending, to the at least one mobile device, a signallingmessage, the signalling message comprising CSI (Channel StateInformation) process data that indicates a plurality of combinedmeasurements to be made by the mobile device, wherein the combinedmeasurement is associated with a respective different configuration ofthe plurality of transmission points and the combined measurementcomprises at least one signal quality measurement and at least oneinterference measurement for the associated configuration of theplurality of transmission points; and means for receiving, from the atleast one mobile device, measurement results for a selected one of theplurality of combined measurements and data identifying which one of theplurality of combined measurements the results relate.

The combined measurement may identify: i) a first set of resourceelements on which a signal quality measurement is to be carried out bythe at least one mobile device; and ii) a second set of resourceelements on which an interference measurement is to be carried out bythe at least one mobile device. The first set of resource elements maycomprise at least one NZP (non-zero power) resource element and thesecond set of resource elements comprises at least one ZP (zero-power)resource element.

The network node may further comprise means for configuring theplurality of transmission points in accordance with the CSI process datasignalled to the mobile device.

The measurement results received from the at least one mobile device maycomprise at least one of: a CQI (Channel Quality Indicator) a RI (RankIndicator) and a PMI (Precoding Matrix Indicator).

The network node may further comprise means for controlling thecoordinated transmissions, by the plurality of transmission points, independence upon the measurement results received from the at least onemobile device.

The data identifying which one of the plurality of combined measurementsthe results relates may comprise: data identifying the CSI process (‘CSIprocess id’) and data identifying at least one of a transmission point(‘TP id’) and an interference measurement resource (‘IMR id’).

The coordinated transmission points may be configured to coordinatetransmissions in accordance with one or more communication modesselected from the group comprising: i) joint transmission (JT) mode inwhich multiple transmission points send data to the mobile device; ii)CS/CB (Coordinated Scheduling/Beam forming) mode in which the mobiledevice receives transmissions from one transmission point, and thetransmission points coordinate their scheduling and/or beam formingdecisions to minimise interference between the transmissions; and iii)DPS (Dynamic Point Selection) mode in which the mobile device receivestransmissions from a transmission point selected from a set ofcoordinating transmission points.

At least one of the plurality of transmission points may be selectedfrom a group comprising: i) a base station; ii) a RRH (remote radiohead); and a RN (relay node). The network node may comprise a basestation operating in accordance with the LTE (long term evolution) setof standards. At least two cells operated by the plurality oftransmission points may be configured for CA (Carrier Aggregation).

The network node may further comprise means for generating the CSIprocess data.

In another aspect, the present invention provides a mobile device for acommunication system providing coordinated transmissions via a pluralityof transmission points which operate at least one cell, the mobiledevice comprising: means for receiving from a transmission point asignalling message, the signalling message comprising CSI (Channel StateInformation) process data that indicates a plurality of combinedmeasurements to be made by the mobile device, wherein the combinedmeasurement is associated with a respective different configuration ofthe plurality of transmission points and the combined measurementcomprises at least one signal quality measurement and at least oneinterference measurement for the associated configuration of theplurality of transmission points; and means for sending, to atransmission point, measurement results for a selected one of theplurality of combined measurements and data identifying which one of theplurality of combined measurements the results relate.

The mobile device may further comprise a measurement module forobtaining signal quality measurements and interference measurements ofsignals received from different transmission points within the vicinityof the mobile device. The mobile device may further comprise means forconfiguring the measurement module in accordance with the CSI processdata signalled by the transmission point.

The mobile device may be selected from a group comprising: i) a mobiletelephone; ii) a mobile terminal; and iii) UE (user equipment).

In yet another aspect, the present invention provides a network node forcontrolling coordinated transmissions, in a communication systemcomprising at least one mobile device and a plurality of transmissionpoints which operate at least one cell, the network node comprisingtransceiver circuitry for: sending, to the at least one mobile device, asignalling message, the signalling message comprising CSI (Channel StateInformation) process data that indicates a plurality of combinedmeasurements to be made by the mobile device, wherein the combinedmeasurement is associated with a respective different configuration ofthe plurality of transmission points and the combined measurementcomprises at least one signal quality measurement and at least oneinterference measurement for the associated configuration of theplurality of transmission points; and receiving, from the at least onemobile device, measurement results for a selected one of the pluralityof combined measurements and data identifying which one of the pluralityof combined measurements the results relate.

In yet another aspect, the present invention provides a mobile devicefor a communication system providing coordinated transmissions via aplurality of transmission points which operate at least one cell, themobile device comprising transceiver circuitry for: receiving from atransmission point a signalling message, the signalling messagecomprising CSI (Channel State Information) process data that indicates aplurality of combined measurements to be made by the mobile device,wherein the combined measurement is associated with a respectivedifferent configuration of the plurality of transmission points and thecombined measurement comprises at least one signal quality measurementand at least one interference measurement for the associatedconfiguration of the plurality of transmission points; and sending, to atransmission point, measurement results for a selected one of theplurality of combined measurements and data identifying which one of theplurality of combined measurements the results relate.

In yet another aspect, the present invention provides a method performedby a network node for controlling coordinated transmissions, in acommunication system comprising at least one mobile device and aplurality of transmission points which operate at least one cell, themethod comprising: sending, to the at least one mobile device, asignalling message, the signalling message comprising CSI (Channel StateInformation) process data that indicates a plurality of combinedmeasurements to be made by the mobile device, wherein the combinedmeasurement is associated with a respective different configuration ofthe plurality of transmission points and the combined measurementcomprises at least one signal quality measurement and at least oneinterference measurement for the associated configuration of theplurality of transmission points; and receiving, from the at least onemobile device, measurement results for a selected one of the pluralityof combined measurements and data identifying which one of the pluralityof combined measurements the results relate.

In yet another aspect, the present invention provides a method performedby a mobile device for a communication system providing coordinatedtransmissions via a plurality of transmission points which operate atleast one cell, the method comprising: receiving from a transmissionpoint a signalling message, the signalling message comprising CSI(Channel State Information) process data that indicates a plurality ofcombined measurements to be made by the mobile device, wherein thecombined measurement is associated with a respective differentconfiguration of the plurality of transmission points and the combinedmeasurement comprises at least one signal quality measurement and atleast one interference measurement for the associated configuration ofthe plurality of transmission points; and sending, to a transmissionpoint, measurement results for a selected one of the plurality ofcombined measurements and data identifying which one of the plurality ofcombined measurements the results relate.

The invention also provides a communication system comprising the abovedescribed network node and the above described mobile device.

Aspects of the invention extend to computer program products such ascomputer readable storage media having instructions stored thereon whichare operable to program a programmable processor to carry out a methodas described in the aspects and possibilities set out above or recitedin the claims and/or to program a suitably adapted computer to providethe apparatus recited in any of the claims.

Each feature disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently (or in combination with) any other disclosedand/or illustrated features. In particular but without limitation thefeatures of any of the claims dependent from a particular independentclaim may be introduced into that independent claim in any combinationor individually.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the attached figures in which:

FIG. 1 schematically illustrates a mobile telecommunication system of atype to which the invention is applicable;

FIG. 2 a illustrates a generic frame structure defined for use in theLTE communication network;

FIG. 2 b illustrates the way in which a slot illustrated in FIG. 2 a isformed of a number of time-frequency resources;

FIGS. 3 a, 3 b and 3 c schematically illustrate different mobiletelecommunication system scenarios having multiple, coordinated networktransmission points;

FIG. 4 is a block diagram illustrating the main components of the basestation forming part of the system shown in FIG. 1 ;

FIG. 5 is a block diagram illustrating the main components of a mobiletelephone forming part of the system shown in FIG. 1 ;

FIG. 6 illustrates an exemplary IMR configuration according to anembodiment of the present invention; and

FIG. 7 is an exemplary timing diagram illustrating a method performed bycomponents of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 including a mobile telephone 3 (or other compatible userequipment) served via the cells of a plurality of base stations 5-1 to5-3. The telecommunication system 1 also comprises a core network 8. Asthose skilled in the art will appreciate, whilst one mobile telephone 3and three base stations 5 are shown in FIG. 1 for illustration purposes,the system, when implemented, will typically include other base stationsand mobile telephones.

The base stations 5 are connected to each other via a so-called X2interface, and to the core network 8 via an S1 interface. The corenetwork 8 comprises, amongst other things, a mobility management entity(MME) 12, a serving gateway (SGW) 14 and a Packet Data Network (PDN)Gateway (PGW) 16.

As will be understood by those skilled in the art, each base station 5operates one or more base station cells (not shown) in whichcommunications can be made between the base station 5 and the mobiletelephone 3. A user of the mobile telephone 3 can communicate with otherusers and/or remote servers via the base station 5 and the core network8.

LTE Sub-Frame Data Structure

Before discussing the specific ways in which the mobile telephone 3 cancommunicate with the multiple transmission points, a brief descriptionwill be given of the access scheme and a general frame structure agreedfor LTE communications. An Orthogonal Frequency Division Multiple Access(OFDMA) technique is used for the downlink to allow the mobile telephone3 to receive data over the air interface with the base station 5.Different sub-carriers are allocated by the base station 5 (for apredetermined amount of time) to the mobile telephone 3 depending on theamount of data to be sent to the mobile telephone 3. These blocks ofsub-carriers are referred to as physical resource blocks (PRBs) in theLTE specifications. PRBs thus have a time and frequency dimension. Thebase station 5 dynamically allocates PRBs for each device that it isserving and signals the allocations for each sub-frame (TTI) to each ofthe scheduled devices in a control channel.

FIG. 2 a illustrates one generic frame structure agreed for LTEcommunications over the air interface with the base station 5. As shown,one frame 13 is 10 msec long and comprises ten sub-frames 15 of 1 msecduration (known as a Transmission Time Interval (TTI)). Each sub-frameor TTI comprises two slots 17 of 0.5 ms duration. Each slot 17 compriseseither six or seven OFDM symbols 19, depending on whether the normal orextended cyclic prefix (CP) is employed. The total number of availablesub-carriers depends on the overall transmission bandwidth of thesystem. The LTE specifications define parameters for system bandwidthsfrom 1.4 MHz to 20 MHz and one PRB is currently defined to comprise 12consecutive subcarriers for one slot 17 (although this could clearly bedifferent). The transmitted downlink signal comprises N_(BW) subcarriersfor a duration of N_(symb) OFDM symbols. It can be represented by aresource grid as illustrated in FIG. 2 b . Each box in the gridrepresents a single sub-carrier for one symbol period and is referred toas a resource element (RE). As shown, each PRB 21 is formed from twelveconsecutive sub-carriers and (in this case) seven symbols for eachsubcarrier; although in practice the same allocations are made in thesecond slot 17 of each sub-frame 15 as well.

In the case of carrier aggregation, multiple carriers are provided, eachhaving the frame structure illustrated in FIGS. 2 a and 2 b , butseparated in frequency so that they do not interfere.

Some of the resource elements are configured to carry the referencesignals used for signal quality measurements. Similarly, some of theresource elements can be transmitted at zero power level forfacilitating the above described interference measurements. The CSIprocess informs the mobile telephone 3 which resource elements of whichcarriers are currently configured to carry the NZP CSI-RS and ZP CSI-IMsignals to be measured and reported.

In this embodiment, the base stations 5 are arranged to be able tocommunicate with the mobile telephone 3 as a number of coordinatedtransmission points. Optionally, one or more of the base stations 5 maybe configured to provide aggregated component carriers. The transmissionpoints (TPs)—the base stations 5 in the embodiments, co-operate togetherto co-ordinate their multi-point transmissions. Typically, differentsets of co-ordinating transmission points will be provided within thecommunications system. A number of different multi-point transmissionmodes are possible, as follows:

-   -   1. Joint Transmission (JT). In this case the mobile telephone 3        receives transmissions from multiple transmission points (TPs)        on a time-frequency resource (such as on a PRB on a sub-frame).        These transmissions may be carrying the same data (such that the        signals from each TP can be combined by the mobile telephone 3        and thereby improve the quality of the received signal) or        different data (such that more data per time-frequency resource        is sent to the mobile telephone 3) from the TPs.    -   2. Coordinated scheduling/beam forming (CS/CB). In this case the        mobile telephone 3 receives transmissions from only one TP on        any one time-frequency resource, and the TPs co-ordinate their        scheduling and/or beam forming decisions to minimise        interference between the transmissions. The transmitting points        that are used are chosen semi-statically—such that they change        relatively infrequently.    -   3. Dynamic Point Selection (DPS). In this case the mobile        telephone 3 receives transmissions on a time-frequency resource        from only one TP selected from the set of co-ordinating        transmission points; but the selected TP may change rapidly        (from one sub-frame to another) based on the instantaneous radio        channel conditions between the mobile telephone 3 and the        transmission points.

Depending on the number of transmission points, and whether any of thebase stations 5 implement carrier aggregation functionality, there are anumber of cells that need to be measured and reported by the mobiletelephone 3 in order to assist the serving base station(s) 5 inoptimising signal conditions within the cells of the communicationsystem 1.

In this embodiment, the serving base station 5 (e.g. base station 5-1)configures the mobile telephone 3 to measure and report the CSI of a setof non-zero power CSI-RS resources (i.e. the CoMP measurement set). Themobile telephone 3 may also be configured with one or more interferencemeasurements. Each interference measurement is associated with oneCSI-interference measurement resource (IMR), which is a set of REs onwhich the mobile telephone 3 is instructed to measure interference.

As specified in the relevant 3GPP standards, a CSI process is identifiedby a CSI process index and a serving cell index. The serving cell indexidentifies the transmission point and a carrier (i.e. a cell of the basestation 5 sending the CSI process to the mobile telephone 3) for whichsignal measurements (on NZP CSI-RS) and interference measurements (on ZPIMR) should be carried out by the mobile telephone 3. E-UTRAN configuresat most five CSI processes across all serving cells (i.e. for up to fivecomponent carriers) in order to keep UE complexity and feedback overheadat a minimum.

However, in this proposal, one CSI process is advantageously associatedwith multiple carriers (i.e. multiple TPs and/or component carriers incase of CA) and multiple IMR configurations. In particular, rather thaneach base station 5 configuring one signal quality measurement and oneinterference measurement per CSI process (i.e. each base stationconfiguring each CSI process for a single carrier only), in thisembodiment, each CSI process can be associated with multipletransmission points and can specify multiple signal quality andinterference measurements. This allows for an increase of the number ofconfigurations without requiring an exchange of additional messagesbetween the base stations 5 and the mobile telephone 3 to configure suchadditional measurements and also without an impact on the CoMPthroughput performance gain. Increasing the number of configurations forthe interference part of CSI can also improve the interferencemeasurement accuracy and performance. On the other hand, if only five(or less) configurations are needed, it is possible to implement themusing less signalling thus essentially saving system resources whichthen can be used to transmit e.g. user data.

When the mobile telephone 3 reports the results of the measurements toone of the CoMP transmission points, it identifies which measurement isbeing reported (rather than just identifying the CSI process). Forexample, the mobile telephone 3 may include in the CSI feedback,reporting information identifying the interference measurement that isbeing reported (e.g. an IMR ID) and/or an index of the combination oftransmission point (or carrier) and IMR (TP/IMR index).

The benefit of this approach is that more measurements can be configuredusing the same amount of messages and it is also possible to configuremeasurements for multiple (or even all) CoMP transmission points (orcarriers) by a single transmission point, in one message. Even whenadditional measurements are configured for (and carrier out by) themobile telephone, since only the results of relevant measurements needto be reported (i.e. carriers on which the UE is experiencing low signalquality and/or high interference), the amount of information (and thenumber of messages) to be sent by the mobile telephone 3 does notincrease (significantly) even when additional measurements have beenconfigured. However, since more interference measurements can beconfigured and performed by the mobile telephone 3 compared to methodsusing a single IMR measurement per CSI process, the accuracy ofmeasurements is likely to increase.

On the other hand, if the same amount of measurements are to beconfigured (i.e. up to five CSI processes as per current 3GPPrequirements), it is possible to configure those measurements usingfewer messages (even in a single message) thus reducing usage of the airinterface resource between the base stations 5 and the mobile telephone3.

Although not shown on FIG. 1 , the telecommunication system 1 may alsocomprise one or more Remote Radio Heads (RRHs) and/or relay nodes (RNs)in addition to (or instead of any of) the base stations 5-1 to 5-3. Ifpresent, the main difference between ‘regular’ base stations 5-1 to 5-3and any RRH or relay node is that RRHs and relay nodes are not connectedto the core network 8 directly. Instead, the RRH is typically connectedto a master (or ‘donor’) base station by a high speed communication linkwhilst relay nodes are typically connected to a donor base station viaan air interface. The RRH and the RN may either act just like a remoteantenna of the base station—such that the signals broadcast by theRRH/RN are the same as those broadcast by its donor base station (e.g.the RRH/RN may use the same cell ID as the ‘donor’ base station's cell)or may act as a base station itself serving user equipment within itsown cell (which in this case may have a different cell ID to that of thecell of the ‘donor’ base station).

CoMP transmission schemes can be generally classified to belong to one(or a combination) of the following four main scenarios:

-   -   1. Homogeneous network with intra-site (i.e. intra base station)        CoMP;    -   2. Homogeneous network with high transmit (Tx) power Remote        Radio Heads (RRHs);    -   3. Heterogeneous network with low power RRHs within the coverage        area of a macrocell (e.g. a base station cell) where the        transmission/reception points created by the RRHs have different        cell identities than the macro cell; and    -   4. Heterogeneous network with low power RRHs within the coverage        area of macrocell (e.g. a base station cell) where the        transmission/reception points created by the RRHs have the same        cell identity as the macro cell.

FIGS. 3 a to 3 c schematically illustrate examples of the main CoMPtransmission scenarios for the provision of multiple, coordinatednetwork transmission points.

FIG. 3 a shows an example for implementing a homogeneous network withintra-site CoMP (scenario 1). In this case, the middle base station maybe configured to perform coordination of multi-point transmissions (bythis and any neighbouring base stations) within the geographical areadefined by the coordinating base station's cells. When transmissions arecoordinated between neighbouring base stations, throughput and/or signalquality along the common cell edge can be improved.

FIG. 3 b shows an example for implementing a homogeneous network withhigh Tx power RRHs, controlled by a single base station (scenario 2). Inthis case, the remote radio heads are connected to the master basestation (shown in the middle) via high-speed optical fiber links. Sucharrangement allows the master base station to perform coordination ofmulti-point transmissions even beyond the geographical area of itscells.

FIG. 3 c shows an example for implementing either one of scenario 3 or 4above. In this case, a heterogeneous network is shown with low powerRRHs within the coverage area of a macrocell (e.g. a master base stationcell). The transmission/reception points created by the RRHs may havedifferent cell identities than the macro cell (scenario 3) or have thesame cell identity as the macro cell (scenario 4). The remote radioheads are connected to the master base station (shown in the middle) viahigh-speed optical fiber links, as above. However, in these scenarios,rather than extending the coordinated geographical area as above, thenumber of radio cells (and hence the available bandwidth) within thegeographical area of the master base station's cell(s) is multiplied.

Relay nodes can be deployed and used to provide additional coverageand/or additional transmission points in generally the same manner asthe RRHs shown in FIG. 3 b . However, relay nodes are typicallyconnected to their respective master base stations (called ‘donor basestations’) using a wireless link (an air interface) rather than anoptical fiber link.

Base Station

FIG. 4 is a block diagram illustrating the main components of a basestation 5 shown in FIG. 1 . The base station 5 is a communications nodeproviding services to user equipment 3 within its coverage area. In theembodiments according to the invention, communications between thevarious base stations 5 and the user equipment 3 are coordinated. Asshown, the base station 5 includes a transceiver circuit 51 whichtransmits signals to, and receives signals from, the mobile telephone 3via at least one antenna 53. The base station 5 also transmits signalsto and receives signals from the core network 8 and other neighbouringbase stations 5 via a network interface 55 (X2 interface forcommunicating with neighbouring base stations 5 and S1 interface forcommunicating with the core network 8). The operation of the transceivercircuit 51 is controlled by a controller 57 in accordance with softwarestored in memory 59. The software includes, among other things, anoperating system 61, a communications control module 63, a CoMP module65, a carrier aggregation module 67, and a CSI process configurationmodule 69.

The communications control module 63 is operable to controlcommunications between the base station 5 and the mobile telephone 3,and the core network devices.

The CoMP module 65 is operable to coordinate multi-point transmissionsbetween the cell(s) of this base station 5 and the mobile telephone 3served by this base station (and any further base station). The CoMPmodule 65 may communicate with corresponding modules of other basestations to ensure that coordination is maintained between the variousbase stations and may also assist the communications control module 63to carry out control of communications using CoMP services.

The carrier aggregation module 67 is operable to set up and maintainaggregated carriers (i.e. primary and secondary component carriers) forcommunications between the cells of this base station 5 and the mobiletelephones 3 served by the base station 5.

The CSI process configuration module 69 is operable to configure signalquality indication and interference related measurements and reportingfor the mobile telephones 3 served by this base station 5. The CSIprocess configuration module 69 is also operable to monitor (e.g. viathe CoMP module 65 and the carrier aggregation module 67) whether or notany cell of the base station 5 is involved in provision of CoMP and/orCA services, and to configure CSI processes for the mobile telephones 3accordingly.

Mobile Telephone

FIG. 5 is a block diagram illustrating the main components of the mobiletelephone 3 shown in FIG. 1 . As shown, the mobile telephone 3 has atransceiver circuit 31 that is operable to transmit signals to and toreceive signals from a base station 5 via one or more antenna 33. Themobile telephone 3 has a controller 37 to control the operation of themobile telephone 3. The controller 37 is associated with a memory 39 andis coupled to the transceiver circuit 31. Although not necessarily shownin FIG. 5 , the mobile telephone 3 may of course have all the usualfunctionality of a conventional mobile telephone 3 (such as a userinterface 35) and this may be provided by any one or any combination ofhardware, software and firmware, as appropriate. Software may bepre-installed in the memory 39 and/or may be downloaded via thetelecommunications network or from a removable data storage device(RMD), for example.

The controller 37 is configured to control overall operation of themobile telephone 3 by, in this example, program instructions or softwareinstructions stored within memory 39. As shown, these softwareinstructions include, among other things, an operating system 41, acommunications control module 43, a CSI process module 45, and ameasurement module 47.

The communications control module 43 is operable to control thecommunication between the mobile telephone 3 and the base station(s) 5.The communications control module 43 also controls the separate flows ofuplink data and control data that are to be transmitted to the basestation 5. When CA services are in use, the communications controlmodule 43 is operable to control communications via the aggregatedprimary and secondary component carriers. When CoMP services are in use,the communications control module 43 is operable to control coordinatedcommunications between the mobile telephone 3 and the multipletransmission points.

The CSI process module 45 is operable to receive and enforceconfigurations for signal quality indication and interference relatedmeasurements and reporting to assist the serving base station(s) 5. TheCSI process module 45 is operable to communicate with the correspondingmodule (i.e. the CSI process configuration module 69) of the basestation 5.

The measurement module 47 is operable to carry out signal measurementsto determine an indication of signal quality/interference experienced bythe mobile telephone 3. The measurement module 47 is also operable toprovide the results of such measurements to the serving base station(s)5 (via the CSI process module 45 and the transceiver circuit 31).

In the above description, the mobile telephone 3 and the base station 5are described for ease of understanding as having a number of discretemodules (such as the communications control modules, the CoMP module,and the measurement module). Whilst these modules may be provided inthis way for certain applications, for example where an existing systemhas been modified to implement the invention, in other applications, forexample in systems designed with the inventive features in mind from theoutset, these modules may be built into the overall operating system orcode and so these modules may not be discernible as discrete entities.These modules may also be implemented in software, hardware, firmware ora mix of these.

A number of different embodiments will now be described that illustratehow the invention can be put into effect using the mobile telephone 3and base stations 5 (as exemplary transmission points) of FIG. 1 .

Operation—CSI Association with Multiple TP and IMR Configurations

In this embodiment, the mobile telephone 3 is configured to measureinterference on an IMR whilst the base station 5 (the one that isconsidered to be the interfering TP under that hypothesis) transmitsdata symbols on those IMR REs. Within the CoMP coordinating TPs, it isalso possible for the network to transmit non-PDSCH (i.e. non-data)signals on the IMR REs used by the mobile telephone 3 for interferencemeasurement to generate a precise interference scenario (PDSCH standsfor Physical Downlink Shared Channel, i.e. the main downlinkdata-bearing channel in LTE).

Channel Quality Indication (CQI) comprises information signalled by themobile telephone 3 to the serving base station 5 to indicate a suitabledata rate (typically a Modulation and Coding Scheme (MCS) value) fordownlink transmissions. CQI is usually based on a measurement of thereceived downlink Signal to Interference plus Noise Ratio (SINR) andinformation about the mobile telephone's 3 receiver characteristics.Further details about the CQI can be found in 3GPP TS 36.213, section7.2.3.

CQI reporting is an important element of LTE and has significant impacton the system performance. There are two types of CQI reports in LTE:periodic and aperiodic. The periodic CQI report is carried by either thePhysical Uplink Control Channel (PUCCH) or the Physical Uplink SharedChannel (PUSCH), depending on whether or not the mobile telephone 3 hasuplink data to send in the same subframe as the scheduled periodic CQIreport. The aperiodic CQI report, which may be used to provide a moregranular measurement than the periodic one, is transmitted on the PUSCH.

The granularity of the CQI report can be divided into three levels:wideband, UE selected subband, and higher layer configured subband. Thewideband report provides one CQI value for the entire downlink systembandwidth. The UE selected subband CQI report divides the systembandwidth into multiple subbands, then reports one CQI value for thewideband and one differential CQI value for a set of subbands selected(i.e. preferred) by the mobile telephone 3. The higher layer configuredsubband report divides the entire system bandwidth into multiplesubbands, then reports one wideband CQI value and multiple differentialCQI values, one for each subband. This report provides the highestgranularity.

PMI (Precoding Matrix Indicator) and RI (Rank Indication) may also bereported by the mobile telephone 3 together with the CQI report. PMIindicates the codebook (pre-agreed parameters) the base station 5 shoulduse for data transmission over its multiple antennas 53 based on anevaluation of a received reference signal (e.g. RSRP). RI indicates thenumber of spatial transmission layers that the mobile telephone 3 candistinguish. Spatial multiplexing can be supported only when RI>1. Forspatial multiplexing, CQI is reported per codeword.

In order to obtain accurate CQI feedback at the serving base station 5,the mobile telephone 3 needs to send multiple CQI reports with differentinterference hypothesis for the serving TP (e.g. base station 5-1) andfor cooperating TPs (e.g. base stations 5-2 and 5-3) resulting in asignificant feedback overhead. Therefore, CQI reports are typically sentevery few milliseconds (approximately every 5-10 ms for voice traffic,and possibly more often for other types of traffic) and for eachtransmission point (e.g. all of base stations 5-1 to 5-3 and for allcomponent carriers in case of CA). However, too frequent CQI reportingis wasteful of air interface resources that would otherwise be used totransmit user data. Consequently, the more CQI feedback is sent, theless user data can be transmitted over the air interface (althoughsignal quality may improve).

As shown in Table 1, each CSI process includes one NZP CSI-RS and oneIMR for each TP, hence four CQI feedback reports per component carrierfor a CoMP scenario with three TPs would be sent every 5-10 ms. However,for a specific CoMP scheme, such as DPS, DPB or JT, the CoMP scheduler(i.e. the CoMP module 65) of the base station 5 would only need to knowthe full CSI information of one or two of these CSI processes, e.g. thebest one or two of the CSI processes #1, #2, and #3 shown in Table 1.Consequently, the mobile telephone 3 does not need to send all fourpossible CQI feedback reports, only the most relevant ones. The mobiletelephone 3 may include in its CQI feedback report the CQI value(s) forthe subband measurement, the wideband measurement, or both.

TABLE 1 existing configuration of CSI processes (3 TPs, e.g. basestations 5-1, 5-2, and 5-3 of FIG. 1) Signal part Interference Part (NZPCSI-RS) (ZP CSI-RS) IMR Description CSI process #0 TP #1 IMR #1Interference outside cooperating set TP1, TP2 and TP3 are muted (OFF)CSI process #1 TP #1 IMR #2 Muting on TP1 (OFF) TP2 ON, TP3 ON CSIprocess #2 TP #2 IMR #3 Muting on TP2 (OFF) TP1 ON, TP3 ON CSI process#3 TP #3 IMR #4 Muting on TP3 (OFF) TP1 ON, TP2 ON

In this embodiment, in order to achieve more accurate CQI per TP forCoMP feedback without increasing the number of CSI reporting, a singleCSI process (i.e. a CSI process set) is associated with multiple TPs andthis single CSI process includes multiple instances of NZP CSI-RS andmultiple instances of IMR where each NZP CSI-RS instance is linked toone TP and each IMR instance could be linked to one or more TPs.

This scheme can advantageously facilitate vendor specific precodingoptimisation schemes at the transmission point without requiring themobile telephone 3 to be aware of the precise precoding matrix. This isparticularly useful in scenarios where UE specific elevation beamformingis required as in the case of some urban scenarios for Release-12 (e.g.such urban scenarios may include a mixture of skyscrapers, officebuildings and residential buildings, with some mobile telephones 3 beinglocated at ground level and others distributed at various heights in thebuildings).

Table 2 shows an example of the new CSI process configurations for amobile telephone 3 in the case of two transmission points. CSI process#0 and CSI process #1 are designed for this purpose. In this example,TP2 (e.g. base station 5-2) is transmitting (with some random weights)using Rank Indicator (RI) set to 1 and Precoding Matrix Indicator (PMI)set to 1, i.e. RI1/PMI-1, on IMR #1 and using RI set to 1 and PMI set to2, i.e. RI1/PMI-2, on IMR #2.

(The reader is referred to 3GPP TS 36.213 Section 7.2 and 7.2.4 forfurther details of what the RI and PMI are used for.) The mobiletelephone 3 only has to perform interference measurements on theconfigured IMR REs. If only a single TP is configured for a given CSIprocess, the mobile telephone 3 may send back the best CQI report in theCSI process plus the corresponding IMR ID with the lowest measuredinterference (i.e. either IMR #1 or IMR #2 for CSI process #0, andeither IMR #3 or IMR #4 for CSI process #1 of this example), i.e. thePMI that causes the least interference to the reporting mobile telephone3.

TABLE 2 exemplary configuration of CSI processes (2 TPs, e.g. basestations 5-1 and 5-2 of FIG. 1) Signal Part Interference Part (NZPCSI-RS) (ZP CSI-RS) IMR Description CSI TP #1 IMR #1 Muting is on TP1and TP2 is process transmitting at RI1/PMI-1 #0 (CS/CB or DPS) TP #1 IMR#2 Muting is on TP1 and TP2 is transmitting at RI1/PMI-2 (CS/CB or DPS)CSI TP #2 IMR #3 Muting is on TP2 and process TP1 is transmitting at #1RI2/PMI-3 (CS/CB or DPS) TP #2 IMR #4 Muting is on TP2 and TP1 istransmitting at RI2/PMI-4 (CS/CB or DPS)

The primary use case of this scheme is for CQI feedback overheadreduction and to support CoMP across multiple component carriers.Although this approach requires the mobile telephone 3 to computeseveral hypothesis in each CSI process, the complexity of the mobiletelephone 3 is not affected because it is required to carry out the samenumber of computations regardless of whether several hypotheses aredefined in one process (as in this embodiment) or only one hypothesis isdefined per CSI process but there are separate CSI processes for eachTPs (i.e. in case each CSI process includes one configuration only).Beneficially, it is also possible to re-use the PMI value within aparticular CSI process among hypotheses that share the same NZP part sothat the common measurements do not have to be repeated for eachhypothesis (because in this case each hypothesis within any CSI processmeasures the same NZP reference signal and hence it is likely to givethe same result). This can be achieved by configuring an RI/PMIreference process. In this context, the reference process refers to thereference PMI/RI values used for the NZP signal part, not theinterference part (i.e. IMR part) shown in Table 2.

One possible way is to re-use the Release-11 RI/PMI reference process,which can be configured for a dependent CSI process. A dependent CSIprocess is expected to be configured to use the same set of restrictedRIs and/or PMIs with codebook subset restriction as the reference CSIprocess. As long as the total number of hypotheses remains the same, thecomplexity remains fixed and with re-use of PMI within a processcomplexity of the mobile telephone 3 can be further limited.

For a given set of hypotheses (where ‘hypothesis’ means one combinationof TP and IMR), the present proposal reduces reporting overhead (whilstit does not change measurement complexity). As illustrated by the twoexamples below, the present proposal (denoted ‘Case 2’) achieves a lowerreporting overhead than existing methods (denoted ‘Case 1’) with thesame (or possibly reduced) measurement complexity.

CSIProcess TP IMR CASE 1 (legacy, 4 CSI processes, 4 hypotheses) 0 #1 #11 #1 #2 2 #2 #3 3 #2 #4 CASE 2 (this proposal, 2 CSI processes, 4hypotheses) 0 #1 #1 #1 #2 1 #2 #3 #2 #4

Table 3 shows an example of a modified CSI process configuration for amobile telephone 3 in communication with three transmission points (e.g.base stations 5-1 to 5-3), each operating two cells (two componentcarriers, CCs, possibly using carrier aggregation as well). In thiscase, multiple NZP CSI-RS and multiple IMRs are configured for each CSIprocess and each IMR is linked to multiple TPs. However, despite therelatively high number of configured measurements, the mobile telephone3 only needs to feedback a single CQI report for each CSI process.Advantageously, the mobile telephone 3 sends back the highest CQI reportand the corresponding index of the TP/IMR ID combination.

TABLE 3 exemplary configuration of CSI processes (3 TPs, e.g. basestations 5-1, 5-2, and 5-3 of FIG. 1) Interference Signal part Part (NZPCSI-RS) (ZP CSI-RS) IMR Description CSI TP #1, CC0 IMR #1 Interferenceoutside process cooperating set TP1, TP2 #0 and TP3 are muted (OFF) onComponent Carrier 0 TP #2, CC0 IMR #1 Interference outside cooperatingset TP1, TP2 and TP3 are muted (OFF) on Component Carrier 0 TP #3, CC0IMR #1 Interference outside cooperating set TP1, TP2 and TP3 are muted(OFF) on Component Carrier 0 CSI TP #1, CC1 IMR #2 Interference outsideprocess cooperating set TP1, TP2 #1 and TP3 are muted (OFF) on ComponentCarrier 1 TP #2, CC1 IMR #2 Interference outside cooperating set TP1,TP2 and TP3 are muted (OFF) on Component Carrier 1 TP #3, CC1 IMR #2Interference outside cooperating set TP1, TP2 and TP3 are muted (OFF) onComponent Carrier 1

For any number of coordinated transmission points, the CSI processes maybe defined as follows:

CSI-Process-r12: {  CSI-Process-ID Integer  NZP-CSI-RS-ID MultipleInstances  CSI-IM-ID Multiple Instances  ... }

In the above embodiments, each IMR can be configured independently e.g.with an R10 ‘subframeConfig’ and an R10 ‘resourceConfig’, where‘resourceConfig’ is for four REs/PRB.

The benefit of the proposal is that accurate per TP CQI for CoMPfeedback can be achieved without increasing the number of CSI reportingsignalling. The only additional data to be exchanged is the index of theselected IMR, i.e. approximately 2-3 bits of data.

An alternative to the above proposal would be to increase the number ofCSI processes according to the number of transmission points/componentcarriers. However, given the definition of CSI process and CQI feedbackcurrently used in Rel-11, this would result in significantly largerfeedback overhead and increased UE processing complexity.

Operation—CSI-IMR Measurement and Configuration

The current version of the 3 GPP TS 36.213 standard (v11.1.0) specifiesCQI as follows: “Based on an unrestricted observation interval in timeand frequency, the UE shall derive for each CQI value reported in uplinksubframe n the highest CQI index between 1 and 15”.

However, the standard does not specify which CSI-IM REs may be used orhow many IMRs may be used. The set of CSI-IM REs to use for aninterference estimate is currently not specified by 3GPP. Based on thecontents of 3GPP document no. R1-125370, the following observations canbe made:

-   -   the mobile telephone 3 may employ excessive time domain        averaging;    -   it is not clear how much averaging in frequency is allowed; and    -   the absence of RANI guidance on interference leads to        inconsistent UE behaviour and performance loss.

Further, in 3GPP document no. R1-125051 the following observations aremade:

-   -   averaging in time can also degrade the estimation performance;        and    -   averaging interference over multiple IMRs may significantly        increase the CQI error.

The proposed scheme agrees with the existing requirements for CSI-IMR REconfiguration, i.e. that the IMR measurements for a single CSI processshall be as close to each other as possible (i.e. a ‘time domainrequirement’) and that the measurement of the interference part shouldbe within the subband of the signal part (i.e. a ‘frequency domainrequirement’).

The additional IMRs may be configured only on (UE and/or network)selected subbands and the selected TP/IMR index may only need to be sentwhenever there are changes to the selected TP and/or IMR ID.

The density of the IMR configuration can be reconfigured or reduced infrequency domain, e.g. within certain selected sub-band. This allows toachieve a reduction of measurement complexity by reducing the number ofIMR measurement to be performed in the frequency domain.

FIG. 6 illustrates an example where each IMR utilizes four REs from twoPRBs, e.g. IMR-1A uses two REs from PRB0 and two additional REs fromPRB1. In this embodiment, in accordance with section 7.2.6 of 3GPP TS36.213 (v11.2.0), the mobile telephone is configured with four CSI-IMresource configurations.

In particular, the following parameters are configured (e.g. usinghigher layer signalling, e.g. RRC signalling) for each CSI-IM resourceconfiguration:

-   -   Zero-power CSI RS Configuration (as defined in Table 6.10.5.2-1        and Table 6.10.5.2-2 of 3 GPP TS 36.211 (V11.2.0)); and    -   Zero-power CSI RS subframe configuration (as defined in section        6.10.5.3 of 3 GPP TS 36.211 (V11.2.0)).

SUMMARY

In summary, with the embodiments described above, the number ofconfigurable interference hypothesis was increased without increasingthe number of CQI feedback reporting. Each CSI process may be associatedwith multiple serving TPs and multiple IMR configurations with singleCQI feedback indicating the corresponding IMR ID with the highest CQIand/or PMI that causes least interference to the reporting mobiletelephone 3.

FIG. 7 shows an example timing diagram illustrating a method performedby components of the telecommunication system 1 when configuring andperforming signal quality and interference related measurements andreporting.

The process begins in step S701, in which the base station 5-1 providesinformation relating to the possible CSI process configurations to themobile telephone 3. The CSI process configurations, including the IMRconfiguration, are configured by higher layer (e.g. RRC layer)signalling. However, in this embodiment, the mobile telephone 3 onlyreports the hypothesis with the best (one or two) CQI report within eachCSI process rather than all of them. Therefore, the base station 5-1includes in the CSI process configurations, data identifying eachrespective hypothesis (measurement configuration). For example, ahypothesis may be identified using an index of the transmission points(i.e. a ‘TP index’) and/or an index of the corresponding interferencemeasurement resources (i.e. an ‘IMR index’). When the mobile telephone 3subsequently reports the measurement results (e.g. the best CQI report)for a particular CSI process, the IMR index alone (or in combinationwith the TP index) may be sufficient to uniquely identify whichmeasurement configuration (hypothesis) each result relates to.

However, a particular hypothesis may be identified by other methods,e.g. using the CSI index in combination with the TP index and/or the IMRindex as long as the base station 5-1 and the mobile telephone 3 agreeon the method used.

At the end of step S701, the measurement configurations (including thedata identifying each respective hypothesis) are available to therespective modules of the mobile telephone 3 (stored in memory 39) andthe base station 5-1 (stored in memory 59).

In step S703, the CSI process configuration module 69 generates andsends (via the transceiver circuit 51) a ‘CSI Process’ request messageto the corresponding module (CSI process module 45) of the mobiletelephone 3. This message requests the mobile telephone 3 to performsignal quality and interference measurements and reporting for CoMPservices. It does this by including in this message data identifying theCSI process configurations to be used during the measurements, such asan identification of the CSI process, an identification of the resourceelements to be measured to obtain a measure of signal quality (of agiven TP), and/or an identification of the IMR(s) to be measured as partof that CSI process.

In response to receiving the CSI process message, the mobile telephone 3configures, in step S705, its measurement module 47 in accordance withthe received configuration data and starts monitoring signal conditionsas defined therein.

In step S707, the measurement module 47 performs the necessary cellmeasurements (CSI measurements) in respect of the resource elementsidentified in the received configuration data (i.e. it measures NZP RSresource elements in order to obtain a measure of signal quality and itmeasures ZP resource elements in order to obtain a measure ofinterference). Once the measurements are completed, in step S709, theCSI process module 45 generates a CSI measurement report, e.g. asprescribed by the ‘CSI Process’ request message received at step S703and/or in accordance with the specific CoMP scheme being used.

In step S711, the CSI process module 45 sends the generated CSImeasurement report (via the transceiver circuit 31) to the base station5-1 in a CSI report message. This measurement report includes theresults of only those measurements (e.g. one or more CQI value(s)),performed in step S707, that are considered relevant for the specificCoMP scheme being used. The measurement report also identifies thecorresponding hypothesis for each measurement result being reportedusing the agreed identification method for that CSI process, e.g. TPand/or IMR index. The measurements and the associated reportingprocedure (i.e. steps S707 to S711) may be repeated periodically if ithas been requested to do so in the preceding CSI process message.Therefore, a single message at step S703 may trigger multiple, periodicCSI Reports (i.e. step S711 may comprise multiple and/or periodicallysent messages). For example, a new CSI report may be generated and sentwhen a certain amount of time has passed (or a prescribed number ofsub-frames have been transmitted) since sending a preceding CSI reportand/or whenever the results of the relevant measurements are differentto the results informed in a preceding CSI report.

After it has received the results of the relevant measurements andverified which measurement configuration they relate to (using the datastored in its memory 59), the base station 5-1 is operable to controlthe operation of the CoMP service (as generally shown at S713) inaccordance with the received results. For example, the base station 5-1may adjust its transmissions to reduce or eliminate any indicatedinterference. Furthermore, the base station 5-1 may also inform theother cooperating transmission points (e.g. base stations 5-2 and 5-3)if they need to adjust their transmissions in order to achieve betterCoMP performance. The base station 5-1 may either forward the CSImeasurement results to the other transmission points or forward onlythose parts of the CSI measurement results that are relevant to thosetransmission points. Alternatively, the base station 5-1 may provide therequired operating parameters for the other transmission points, therebyeffectively acting as a master base station which controls the operationof other CoMP transmission points as well.

Modifications and Alternatives

Detailed embodiments have been described above. As those skilled in theart will appreciate, a number of modifications and alternatives can bemade to the above embodiments whilst still benefiting from theinventions embodied therein.

In the above embodiments, the base stations (or RRHs/RNs) are describedas transmission points. However, the term ‘transmission point’ shall notbe construed as being limited to network nodes that are actuallytransmitting user data to CoMP enabled mobile telephones—they may onlytransmit control data, such as reference signals and the like.

In the above embodiments, a mobile telephone based telecommunicationssystem was described. As those skilled in the art will appreciate, thesignalling techniques described in the present application can beemployed in other communications system. Other communications nodes ordevices may include user devices such as, for example, personal digitalassistants, laptop computers, web browsers, etc.

In the embodiments described above, the mobile telephone and the basestations will each include transceiver circuitry. Typically thiscircuitry will be formed by dedicated hardware circuits. However, insome embodiments, part of the transceiver circuitry may be implementedas software run by the corresponding controller.

In the above embodiments, a number of software modules were described.As those skilled in the art will appreciate, the software modules may beprovided in compiled or un-compiled form and may be supplied to the basestation or the relay station as a signal over a computer network, or ona recording medium. Further, the functionality performed by part or allof this software may be performed using one or more dedicated hardwarecircuits.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1306100.7, filed on Apr. 4, 2013,the disclosure of which is incorporated herein in its entirety byreference.

The invention claimed is:
 1. A method performed by a user equipment (UE)for a communication network, the method comprising: receiving, from thecommunication network, a radio resource control (RRC) message includingconfiguration information, wherein the configuration informationcomprises: an identifier; a channel state information reference signal(CSI-RS) information element that represents a plurality of CSI-RSresource configurations for reporting a CSI; and a channel stateinformation interference measurement (CSI-IM) information element thatrepresents at least one CSI-IM resource configuration for the reportingof the CSI, wherein the identifier corresponds to both the plurality ofCSI-RS resource configurations and the least one CSI-IM resourceconfiguration; and transmitting, to the communication network, a CSIbased on the configuration information.
 2. The method according to claim1, wherein each of the plurality of CSI-RS resource configurations isassociated with a respective CSI-IM resource configuration.
 3. Themethod according to claim 1, wherein the reporting the CSI is periodicreporting.
 4. The method according to claim 1, wherein the reporting theCSI is aperiodic reporting.
 5. A user equipment (UE) for a communicationnetwork, the UE comprising: a receiver configured to: receive, from thecommunication network, a radio resource control (RRC) message includingconfiguration information, wherein the configuration informationcomprises: an identifier; a channel state information reference signal(CSI-RS) information element that represents a plurality of CSI-RSresource configurations for reporting a CSI; and a channel stateinformation interference measurement (CSI-IM) information element thatrepresents at least one CSI-IM resource configuration for the reportingof the CSI, wherein the identifier corresponds to both the plurality ofCSI-RS resource configurations and the least one CSI-IM resourceconfiguration, and a transmitter configured to transmit, to thecommunication network, a CSI based on the configuration information. 6.The UE according to claim 5, wherein each of the plurality of CSI-RSresource configurations is associated with a respective CSI-IM resourceconfiguration.
 7. The UE according to claim 5, wherein the reporting theCSI is periodic reporting.
 8. The UE according to claim 5, wherein thereporting the CSI is aperiodic reporting.
 9. A method performed by abase station comprising: transmitting, to a user equipment (UE), a radioresource control (RRC) message including configuration information,wherein the configuration information comprises: an identifier, achannel state information reference signal (CSI-RS) information elementthat represents a plurality of CSI-RS resource configurations forreporting a CSI, and a channel state information interferencemeasurement (CSI-IM) information element that represents at least oneCSI-IM resource configuration for the reporting the CSI, wherein theidentifier corresponds to both the plurality of CSI-RS resourceconfigurations and the least one CSI-IM resource configuration, andreceiving, from the UE, a CSI based on the configuration information.10. The method according to claim 9, wherein each of the plurality ofCSI-RS resource configurations is associated with a respective CSI-IMresource configuration.
 11. The method according to claim 9, wherein thereporting the CSI is periodic reporting.
 12. The method according toclaim 9, wherein the reporting the CSI is aperiodic reporting.
 13. Abase station comprising: a transmitter configured to: transmit, to auser equipment (UE), a radio resource control (RRC) message includingconfiguration information, wherein the configuration informationcomprises: an identifier; a channel state information reference signal(CSI-RS) information element that represents a plurality of CSI-RSresource configurations for reporting a CSI, and a channel stateinformation interference measurement (CSI-IM) information element thatrepresents at least one CSI-IM resource configuration for the reportingthe CSI, wherein the identifier corresponds to both the plurality ofCSI-RS resource configurations and the least one CSI-IM resourceconfiguration, and a receiver configured to receive, from the UE, a CSIbased on the configuration information.
 14. The base station accordingto claim 13, wherein each of the plurality of CSI-RS resourceconfigurations is associated with a respective CSI-IM resourceconfiguration.
 15. The base station according to claim 13, wherein thereporting the CSI is periodic reporting.
 16. The base station accordingto claim 13, wherein the reporting the CSI is aperiodic reporting.